he used to write a column in Sing out magazine..
you can probalby see it on their web page...
and you could probably forward a letter to
him thru the magazine...or thru his record
label. The best way you can honor his is to
actively do some thing to improve your town,
your life or your environment and then you
would have something to write to him about!

see this article for insiration:
http://www.appleseedrec.com/theorchard/winter06/peteseeger.html